The use of assisted reproductive technology is believed to be one cause of the rising incidence of multi-fetal gestations. These multiple births more often result in preterm delivery, low birthweight, and associated neonatal morbidity and mortality. The study will address the following specific aims; 1) describe the factors in the mother's infertility that led to the need for assisted reproduction; 2) report the specific methods that led to the pregnancy; 3) compare the maternal risk factors, prenatal and intrapartum events, maternal, neonatal and post-natal outcomes (up to one year of age) and health care utilization for multiple pregnancies conceived through assisted technology with those conceived spontaneously. The study design is a retrospective cohort study. Mothers with multiple gestations will be drawn from a large database of Kaiser Permanente patients who delivered after 20 weeks gestation between January 1994 and December 1999. Exposed patients (called "cases" in the proposal) are women who conceive as a result of assisted reproduction (ovulation induction and IVF). Non-exposed patients (called "controls" in the study) are defined as multiple gestations conceived spontaneously. Data will be extracted from numerous administrative databases, prenatal records, infant records, and chart reviews. Numerous maternal and neonatal outcomes will be evaluated to determine if multiple pregnancies conceived with assisted reproduction are at higher risk for adverse outcomes when compared to pregnancies conceived spontaneously.